The overall objective of this study is to explore psychosocial processes as possible cofactors in the development of the acquired immune deficiency syndrome (AIDS) in an at-risk population. The specific objectives are: 1) to understand how individuals appraise, respond emotionally to and cope with the risk of developing AIDS, 2) to determine if particular psychological responses to the risk of AIDS are associated with the practice of AIDS risk-reducing behaviors, 3) to determine if particular psychological responses to the risk of AIDS are associated with changes in the immune system (rapid reductions in helper/inducer T cell levels, and altered immune response to the AIDS virus) and increased likelihood of developing AIDS and 4) to determine if exposure to stressful life situations and particular psychological responses to these situations, are associated with immune changes and increased likelihood of developing AIDS. Fifteen hundred healthy homosexual men are now participating in the Multi-Center AIDS Cooperative Study (MACS). These men are examined every six months for signs and symptoms of AIDS and the AIDS-Related Complex (ARC), seropositivity for the human immunodeficiency virus (HIV), specimen collection and assay of T cell sub-populations, and the gathering of data on potential cofactors in the development of AIDS. The proposed study will add the questionnaire assessment of psychosocial factors (appraisal and response to AIDS risk, other life stress, affect, social support, personal resources) to the examination every six months. A sub-sample of two hundred subjects will participate in a psychological assessment interview at each MACS examination to assess more fully emotional responses and coping strategies used in relation to the AIDS risk and other stressful situations. Intensive immunological assessments will be conducted on this sub-sample. Data analyses will determine whether psychological factors predict the practice of risk-reducing behaviors in HIV seropositive and seronegative subjects. In HIV seropositive individuals, data analyses will determine whether psychosocial factors, in conjunction with other possible cofactors, predict changes in immune response over time and the development of ARC and AIDS.